Melt spinning process of polyamides



Oct. 3, 1967 Filed March 16, 1964 F. SICLAR! ET AL 3,345,445

MELT SPINNING PROCESS OF POLYAMIDES 3 Sheets-Sheet 1 I'll g INVENTORS FRANCESCO SICLARI ANGELO BELLANO LUIGI CIQERI BRUNO DALO PIERLUIGI PERAZZON! PIERO GIACOBONE,DECEASED m ADMINISTRATRIX BY AMILIA MANFREDINI GIACOBONE & M/wr Oct. 3, 1967 F. SICLAR! ETAL 33 9 MELT SPINNING PROCESS OF POLYAMIDES Filed March 16, 1964 5 Sheets-Sheet 2 INVENTORS 4O FRANCESCO SICLARI ANGELO BELLANO LUIGI CI CERI BRUNO DALO PIERLUIGI PERAZZONI PIERO GIACOBONEDECEASED AMILIA MANFREDINI GIACOBONE ADMINISTRATRIX Get. 3, 1967 F. SECLARI ETAL 3,345,445

MELT SPINNING PROCESS OF POLYAMIDES Filed March 16, 1964 3 heets-Sheet 3 I T-C b INVENTORS 53 FRANCESCO SICLARI ANGLO BELLANO LUIGI CICERI BRUNO D'ALO PIERLUIGI PERAZZONI PIERO GlACOBONEpEcEAsw BY EMILIA MANFREDINI GIACOBONE ADMINISTRATRIX B Y awk/M United States Patent 3,345,445 MELT SPINNING PROCESS OF POLYAMIDES Francesco Siclari and Angelo Bellano, Cesano Maderno,

Luigi Ciceri, Como, and Bruno DAlo and Pierluigi Perazzoni, Palazzolo Milanese, Italy, and Piero Giacobone, deceased, late of Milan, Italy, by Emilia Man- 'fredini widow Giacobone, administratrix, Milan, Italy, assignors to Snia Viscosa Societa Nazionale Industria Applicazioni Viscosa S.p.A., Milan, Italy, a company of Italy Filed Mar. 16, 1964, Ser. No. 352,394 Claims priority, application Italy, Mar. 15, 1963,

5,402/ 63, Patent 689,700 6 Claims. (Cl. 264-176) The present invention relates to an improvement in the processes for the melt spinning of polyamides and particularly of polycaproamides, that is of caprolactam polymer, normally known as nylon 6.

In melt spinning of polyamides and particularly of nylon 6, the polymer is usually prepared in form of chips which are subjected to a very thorough drying. The dried chipsare then put into a tank from which they are continuously fed to a melt-spinning head of any known type, for example of the type described in the Italian Patent of du Pont 'No. 376,200 or in the Italian patent of the applicants No. 492,712, or alternatively to a screw type apparatus for melt spinning or to any other known type of melt spinning apparatus.

Generally, in the spinning apparatus, oxygen is excluded and thus spinning is efiected under at atmosphere of inert gas preferably under nitrogen, which is usually allowed to flow through the spinning head, and fills the feed tank of the spinning head.

Drying is normally carried out at 0.1 mm. Hg vacuum and at a temperature between 80 C. and 110 C. until the residual humidity of the chips is not more than 0.15%

Generally one of the main problems in melt spinning is to obtain yarns of regular characteristics concerning some properties, particularly the morphological properties i.e. the regularity of the count, and the chemical aflinity for dyes, i.e. the regularity of dyeing properties.

Now it has been surprisingly found that the regularity of dyeing properties and the regularity of the count of the yarn obtained by a normal melt spinning apparatus, are very much affected by the temperature to which the chips are charged into the feed tank of the spinning head. In modern industrial processessuch temperature lies not far below the final temperature of the drying phase, because in continuous operation the dried polymer is charged into the spinning apparatus immediately, after the drying step, thus avoiding uneconomic interruptions.

More specifically, according to the invention the polymer is charged into the tank of the spinning apparatus at a temperature not more than 50 C. and preferably between 25 and 30 C.

Surprisingly, it has been noticed that the temperatures are critical both as tothe regularity ofdyeing properties and as to the regularity of the count; such a circumstance is surprising because the temperature was not expected to be critical neither in connection with any one of these effects, nor in connection with Both effects considered jointly as there is no known relation between the count regularity and the dyeing properties. v

While the application does not want in any way to be limited to an interpretation of the phenomenon and to terpretation of such effect may be connected with th following phenomenon.

' Because the polymer chips are in contact with the stream of inert gas during the transport to the melt spinning apparatus and in the apparatus itself, it is thought that such contact might cause a variation in the number of the end group of the polymer itself at a relatively high temperature. This variation would influence the dyeing properties of the product.

The influence that would be exerted by such variation on the count regularity is not very clear but, since it has been surprisingly noticed that the dyeing properties and the count regularity seem to be in a way connected at least in relation to this operation, the applicants think that the variaion of the end groups may have some influence also on the count regularity.

The temperatures indicated in the present invention, would therefore represent critical values, below which the number of the polymer end groups becomes stable and cannot be affected by-subsequent inevitable treatments prior to the melting of the chips.

The invention will be better understood by the description of the following non limitative examples.

The treated polymer is nylon 6 obtained by the polymerization of caprolactam by the known methods.

Such polymer is a polyamide that shows a minimum intrinsic viscosity of 0.85 in a m-cresol solution at 20 C. and preferably an intrinsic viscosity comprised between 1.0 and 1.30 which corresponds to a ponderal average molecular weight, calculated with the formula Mfl:16600(!]) (Grieth e Sieber, Faserforshuug und Textiltecknik 6 32, 1955), between 17,300 and 26,000.

The polymer is obtained in the form of chips of suitable size which are fed to a melt spinning head by any known method. For instance, the polymer can be meltextruded as a filament with a 3 to 4 mm. diameter, and said filament can be cut into chips of the magnitude of 2 to 6 mm., or the polymer can be extruded in the form of a ribbon or of sheets, which are then suitably chopped The chips have generally a weight of between 0.005 and 0.04 gr. Said chips, which are considered as starting material according to the present invention are subjected to normal drying, which is carried out under vacuum and at not very high temperatures so as to prevent the oxidation and degradation of the polymer. Preferably, vacuum is maintained between 0.05 and 0.2 mm. Hg and temperature between C. and C.

In order to illustrate the objects of the invention there are included in this application drawings, wherein:

FIG. 1 is a longitudinal section of a drying apparatus;

FIG. 2 is a diagrammatic view illustrating how the hot and dried chips may be cooled outside the tumbler of FIG. 1;

FIG. 3 is a diagrammatic view illustrating another type of apparatus for cooling the chips; and

FIG. 4 is a vertical sectional view of the feed tank into which the cooled chips are delivered, and the spinning head connected thereto.

In FIG. 1 there is shown a rotative tumbler 10 provided with a heating jacket 11, a hatchway 12 for the charge and discharge of the chips and a manometer 13. The tumbler is held eccentrically at two diametrically opposite ends by trunnions 14 and 15, of which the trunnion 15 is provided with a pulley 16 connected to a motor which is not illustrated. In order to carry out the drying process hot water is caused to circulate from a boiler, not shown in the figure, through the valve 17, the coaxial tube 18 and the feeding tube 19 into the jacket 11. The hot water penetrates into the jacket 11 at point 20, comes out through the discharge pipe 21, the coaxial tube 22 and the valve 23, and is then recycled.

During the drying phase the tumbler is connected to a vacuum pump, not shown in the figure, through the coaxial piping 24 and the valve 25.

When the drying step is over, the cooling phase is started, cold or suitably cooled water being introduced into the jacket 11 through valve 26 and pipings 18, 192, 20, 21, 22; it then comes out through the valve 27.

During the cooling operation the vacuum pump is detached from the tumbler by closing the valve 25; the reduced pressure in the tumbler is raised to atmospheric pressure by introducing an inert gas, for instance nitrogen with controlled humidity not more than 70 mgr./m. through the valve 28 and the same coaxial tube 24. Em ploying the equipment of FIG. 1, drying can be carried out at 80 C. and at reduced pressure of 0.1 mm. Hg over a period of about 30 hours.

The cooling of hot and dried chips can also be achieved outside of the tumbler by other means as, for instance, by the devices schematically illustrated in FIGURES 2 and 3. Operating with the device of FIG. 2, the hot and dried chips are discharged from the tumbler on a conveyor belt 32, through a hopper 30 into a cavity filled with inert gas, for instance nitrogen at controlled humidity, not more than 70 mgr./m. contact with air being excluded. This belt is made of a continuous strip of a large mesh fabric moved by two wheels 32 and 33 and running between two slits 34 and 35, so as to divide the space of the equipment in two zones 36 and 37 by suitable devices.

A cooled stream of nitrogen at controlled humidity, not more than 70 mgr./m. is forced from the space 36 to the space 37, thus crossing the layer formed by the polymer chips, which, at the end of its path, has a lower temperature that is fully determined by the conditions chosen for the operations.

The cooled polymer falls from the conveyor belt into a hopper 38 provided with a discharge wheel 39 which prevents the inert gas from escaping.

Under the discharge wheel, the chips are carried by a dry, inert gas through a pneumatic tube 40 into the feed tank 41 of FIG. 4.

The device schematically shown in FIG. 3, can be, for instance, another type of device for cooling the chips.

The dry and hot chips are discharged from the tumbler through a hopper 42 and the valve 43, onto a metallic plate 44 cooled by a cold water stream.

The polymer is caused to run over the entire length of such plate, by the vibration of vibrator 45 applied to the plate, while being covered by an atmosphere of inert gas, as for example nitrogen flowing from the tube 49.

At the end of their path, the chips fall into the hopper 46 and are carried by a dry inert gas stream, through a pneumatic tube 40, into the feed tank 41 of FIG. 4.

According to the first described way of carrying out the present invention, once drying is completed, the chips contained in the tumbler are allowed to cool in the latter by introducing dry nitrogen into the tumbler until atmospheric pressure is attained, followed by introduction of cold water into the jacket of the tumbler at a temperature between C. and 30 C. in substitution of hot water.

Under these conditions at treatment of from 2 to 15 hours is generally sufficient to heat the chips to the temperature desired i.e. to 20-40" C., or to a temperature :at least less than 50 C. The cooled chips are now fed to the spinning equipment of- FIG. 4. In this figure, numher 41 represents a feed tank to which the chips are charged.

Said tank is a cylindrical container supplied with a discharge hopper 42 and a valve 43 through which the chips are fed to the melter 44.

The chips are charged into the feed tank by the known equipment and devices, thus they are charged through a hatchway 45, preferably pneumatically; that is, the chips are conveyed by a nitrogen stream, which enters through the said hatchway and flows out through a discharge mount 46 to be recycled.

The pipe 47, provided with the valve 48 is set to keep under pressure of nitrogen the whole equipment at the starting of the spinning and to discharge it at the end of the spinning.

The tank or silo 41 is provided with three thermometers, a-b-c, whose bulbs penetrate into the polymer.

Under the feed tank there is placed the spinning head 44, which is of the type described for instance in the Patent No. 492,712 mentioned, the lower part of which has a substantially taper shape and forms the melting chamber.

In the wall of this melting chamber the openings 50 and 51 are provided for the inert gas to circulate inside.

The taper wall of the melting chamber is heated by means of the jacket 52, and forms one of the heating surfaces.

The lower outlet of the melting chamber is closed by a nonheated grid to prevent solid chips of polymer from passing beneath said melting chamber. The outlet of this chamber is connected to a pipe 53 which is suitably connected to one or more spinnerettes.

Other heating bodies 54 of any suitable form, are placed inside the melting chamber, the surfaces of said bodies are to be kept at a relatively high temperature in order to heat the liquid polymer surrounding such heating bodies to the desired extent and to melt any-solid particles which may come in contact with said bodies.

It is clear that the heating bodies are to be kept at a distance greater than the maximum size of the largest chips of polymer, and they should not prevent the polymer chips mixed with the liquid' from advancing, such chips being inclined to precipitate by gravity. The type of spinning head of the melting chamber, the spinnerettes as well as the relative pumps and various connections used are not critical and since they are not a part of the invention, any type known can be used, for instance, the spinning head could be provided With'a melting tubular grid or any other type of melt spinning head known could be used.

The following spinning operations have been carried out by use of the above described apparatus:

Example 1 An amount of 2500 kg. of chips (made of small cylinders of resin of 2 mm. diameter and 3 mm. length) are dried in the tumbler dryer of FIG. 1, which has an internal diameter of 200. cm. and a length of 300 cm., at the temperature of C. by step-wise removal of the air and the humidity under a vacuum of 1.5 m. Hg.

The operation is carried out easily by slowly rotating the tumbler around an axis passing through a diagonal.

The humidity, which in the chips charged was 8.5%, is uniformly lower to 0.075% through the entire amount of chips.

When drying is completed, pure nitrogen containing amounts of H 0 not greater than 70 mrngL/mm. of nitrogen is introduced into the tumbler, until the atmospheric pressure is attained.

By means of an air-tight container filled with nitrogen or by means of continuous cup conveyors, pneumatics conveyors etc., the polymer is conducted from the inert gas dryer into the silo set over the melter, as in FIG. 4, where, it feeds the melter by gravity. The internal diameter of the silo is 150 cm. and the height 230 cm. The silo is supplied with three thermometers a-b-c, the bulbs of which penetrate into the polymer; after the charge, they indicated the following temperatures respectively:

C. a 95 b 92 24 hours later the teperatures in the silo were as follows:

C. a (no more in contact with the polymer) 30 b 45 48 hours later:

. C. a (no more in contact with the polymer) 27 32 During spinning, about 300 N l. of pure nitrogen like that introduced in the tumbler, have been allowed to pass inside the melter.

Samples of threads extruded from the heads with the melter of the melters considered, and drawn under standard conditions by a draw-twisting machine, have been wound up as cops of yarn.

A number of cops, thus obtained at successive intervals of time and derived from fractions of the polymer which were successively melted during the course of the spinning operation, are wefted by means of a shuttle loom on a warp according to a picking called saglia. The fabric so obtained was dyed with the following dyes:

Solid xylene blue PB 1%. Light alizarin blue 2G 1%. Sulphonine scarlet CWL 1%.

and it shows a slightly different absorption of the dyes which is detectable by an experienced eye. In particular it has been frequently noticed that the absorption of the dye is more evident in the cops obtained by extrusion of the polymer at the beginning of the, operation.

The count regularity has been evaluated as follows:

The part of the yarn which shows a count that does not present any waste greater than i-1% on the normal count, is considered to be in count.

The percentage of the yarn found out of count has been 12-13%.

The experiment has been repeated under the said conditions, with following exception.

Once the drying is through and the nitrogen is let into the tumbler, to attain atmospheric pressure, the rotation is continued, while, the hot stream of water is replaced in the jacket by a cold stream, for instance, of water at 15 C.

After 3 hours of rotation the temperature of the chips reaches 36 C. throughout the mass while the humidity content is of 0.075%

After charging the polymer in the silo, the following temperatures can be read on the thermometers a-b-c:

The spools of yarn drawn were wound up in the same periods and were woven under the equivalent conditions described in the previous experiment; then they were dyed in the same coloring baths mentioned before, and show a very slightly different absorption of dye which, however, is not easily detectable even by an experienced eye.

The percentage of the out of count yarn has dropped to 0.5%

Example2 An amount of 2500 kg. of chips (made of small resin cylinders with 2 mm. diameter and 3 mm. length) are dried in a tumbler dryer at a temperature of C. by gradually removing the air and the humidity under a vacuum of 1.5 mm. Hg.

The operation is easily carried ,out by slowly rotating the tumbler about an axis passing through a diagonal. The humidity that in the starting chips reached 8.5% is lowered to 0.075 throughout the mass of chips.

When drying is completed, the tumbler is set to atmospheric pressure by introducing pure nitrogen containing amounts of H 0 not greater than 70 rnmgr/mm. of nitrogen.

When the drying phase is through and atmospheric pressure is attained inside the tumbler, the slow rotation is continued, while the hot stream in the jacket is replaced for instance, by a cold stream of water at 15 C.

After 3 hours of rotation the temperature of the chips reaches 36 C. throughout the mass while the humidity content is of 0.075%.

After charging of polymer in the silo, the following temperatures can be read on the thermometers a b-c:

4 monofilament yarns, of 15 denier drawn count are spun at the speed of 800 mt./1.

24 hours later the following temperatures are observed:

The spools of drawn yarn, wound up and dyed as in the Example 1, show a very slightly different dye absorption which, however, is not easily detectable even by the most experienced eye; whereas when repeating the same operations without previously cooling the chips the differences of absorption are very appreciable, considering as out of count the yarn portions whose count has wastes greater than :L3.6% in respect to the normal count; the percentage of the out of count yarn, when cooling the chips, is of 0.6%, whereas it rises to 12.5% when cooling is not carried out. I

What is claimed is:

1. In a process for melt-spinning linear polyamides, wherein the polyamide in chip form is pre-heated from 80 C. to C. and subjected to subatmospheric pressure for thorough drying thereof, and the dried chips are subsequently transferred in an inert dry gas atmosphere to a feed device for melt spinning apparatus for meltspinning thereof, the improvement comprising cooling the chips at a temperature not over 50 C. after they have 7 een dried "and prior to their transfer to said feed device 31' melt spinning apparatus.

2. The process claimed in claim 1, wherein the dried hips are cooled during transferral to said feed device for 1elt spinning apparatus.

3. The process claimed in claim 1. wherein the chips re cooled to a temperature between 25 and 30 C. during heir transfer to said feed device for melt spinning aparatus.

4. The process claimed in claim 1, wherein the chips .re preheated while being subjected to subatmospheric ressure. V

5. The process claimed in claim 2, wherein cooling is :ifected by contacting the chips with a stream of inert gas at controlled humidity during transfer.

6. The process claimed in claim 5, wherein the humidity f the inert gas does noteXceed 70 mgr/m. of inert gas.

8 References Cited UNITED STATES PATENTS OTHER REFERENCES Nylon Production Technique is Unique by I. A. Lee,

10 Chemical and Metallurgical Engineering, March 1946,

ALEXANDER BRODMERKEL, Primary Eqcgminer.

15 ROBERT F. WHITE, Examiner.

J. H. WOO, Assistant Examiner. 

1. IN A PROCESS FOR MELT-SPINNING LINEAR POLYAMIDES, WHEREIN THE POLYAMIDE IN CHIP FORM IS PRE-HEATED ROM 80*C. TO 120*C. AND SUBJECTED TO SUBATMOSPHERIC PRESSURE FOR THOROUGH DRYING THEREOF, AND THEDRIED CHIPS ARE SUBSEQUENTLY TRANSFERRED IN AN INERT DRY GAS ATMOSPHERE TO A FEED DEVICE FOR MELTSPINNING APPARATUS FOR MELTSPINNING THEREOF, THE IMPROVEMENT COMPRISING COOLING THE CHIPS AT A TEMPERATURE NOT OVER 50*C. AFTER THEY HAVE 